1. Field of the Invention
THIS INVENTION concerns ventilators for inducing or assisting lung function in human patients.
2. Background Discussion and the Prior Art
For certain applications there is a requirement for a resuscitator/ventilator system that is sensitive to any spontaneous breathing efforts by the patient so as to respond to such efforts by modifying or inhibiting the operation of the system so that it does not hamper or conflict with the patient's attempt to breathe spontaneously. There are several known systems having this characteristic and two of the more well known are, the so-called Synchronised Intermittent Mandatory Ventilation (SIMV) and Mandatory Minute Ventilation (MMV) systems.
For practical utility, any such system should provide high flows with low levels of patient inspiratory effort ("demand pressure"). One arrangement for supplying breathable gas to a patient in response to a spontaneous breathing effort is to use a conventional demand valve such as used in airmen's breathing apparatus and diving equipment, this being connected in parallel with a conventional ventilator and so arranged that during the exhalation phase of the ventilator cycle, the patient can demand an inhalation volume as required.
The other required function of such a system is to modify or inhibit the ventilator action if a patient inhalation demand at the correct level occurs. However, when a demand valve is used to provide the flow for spontaneous breathing the use of a further demand detector to generate a signal to modify or inhibit the ventilator action would decrease its sensitivity.